It's a known thing with any Daihatsu model. The lambada/O2 sensors usually last C. 40K miles or greater. If you are replacing one now, it's bound that the other one will fail as well. So you might as well get both done. Be careful with the one On the exhaust, as over time the connection might have corroded, so it might have to be an exhaust off and on a bench vice job to get it off.

Edited to add the following;

The O2 sensors are different models to each other, so make sure you fit the correct one to the correct area. As a rule usually a yellow wired one will be in the engine bay before the manifold. And the white cabled one fits to the exhaust under the car. Also make sure you know your engine type before ordering. I.e k3-ve etc.... 1.3 litre as an example as each engine type there is a specific part number for.